“Sometimes we think fear ought to be classed with stealing. It seems to cause more trouble.” (Page 67, Big Book)
Resentment flows from the perception that something has thwarted or is thwarting my plans.
Fear flows from the perception that something might thwart my plans.
These map onto the past and present, on one hand, and onto the future, on the other hand.
They need not, however; one can resent something in the future if it is certain; one can fear something in the past or present if it is speculative.
The real difference between the two, therefore, is not one of timeframe but of certainty. Resentment flows from the certain. Fear flows from the speculative.
Resentment is less emotionally distressing: it is circumscribed by the certain facts.
Fear is too much to handle, because the branching system of possibilities contains too much complexity and too many things to deal with at once.
Give me resentment any day.